Global and regional atmospheric measurements and modeling can play key roles in discovering and quantifying unexpected nascent emissions of environmentally important substances. We focus here on ...three hydrochlorofluorocarbons (HCFCs) that are restricted by the Montreal Protocol because of their roles in stratospheric ozone depletion. Based on measurements of archived air samples and on in situ measurements at stations of the Advanced Global Atmospheric Gases Experiment (AGAGE) network, we report global abundances, trends, and regional enhancements for HCFC-132b (Formula: see text), which is newly discovered in the atmosphere, and updated results for HCFC-133a (Formula: see text) and HCFC-31 (Formula: see textClF). No purposeful end-use is known for any of these compounds. We find that HCFC-132b appeared in the atmosphere 20 y ago and that its global emissions increased to 1.1 Gg⋅y
by 2019. Regional top-down emission estimates for East Asia, based on high-frequency measurements for 2016-2019, account for ∼95% of the global HCFC-132b emissions and for ∼80% of the global HCFC-133a emissions of 2.3 Gg⋅y
during this period. Global emissions of HCFC-31 for the same period are 0.71 Gg⋅y
Small European emissions of HCFC-132b and HCFC-133a, found in southeastern France, ceased in early 2017 when a fluorocarbon production facility in that area closed. Although unreported emissive end-uses cannot be ruled out, all three compounds are most likely emitted as intermediate by-products in chemical production pathways. Identification of harmful emissions to the atmosphere at an early stage can guide the effective development of global and regional environmental policy.
For many years, the comparability of measurements obtained with various
instruments within a global-scale air quality monitoring network has been
ensured by anchoring all results to a unique suite of ...reference gas mixtures,
also called a “primary calibration scale”. Such suites of reference gas
mixtures are usually prepared and then stored over decades in pressurised
cylinders by a designated laboratory. For the halogenated gases which have
been measured over the last 40 years, this anchoring method is highly
relevant as measurement reproducibility is currently much better (< 1 %,
k = 2 or 95 % confidence interval) than the expanded uncertainty of a
reference gas mixture (usually > 2 %). Meanwhile, newly emitted
halogenated gases are already measured in the atmosphere at pmol mol−1
levels, while still lacking an established reference standard. For compounds
prone to adsorption on material surfaces, it is difficult to evaluate mixture
stability and thus variations in the molar fractions over time in cylinders
at pmol mol−1 levels. To support atmospheric monitoring of halogenated gases, we create new primary
calibration scales for SF6 (sulfur hexafluoride), HFC-125
(pentafluoroethane), HFO-1234yf (or HFC-1234yf,
2,3,3,3-tetrafluoroprop-1-ene), HCFC-132b (1,2-dichloro-1,1-difluoroethane)
and CFC-13 (chlorotrifluoromethane). The preparation method, newly applied to
halocarbons, is dynamic and gravimetric: it is based on the permeation
principle followed by dynamic dilution and cryo-filling of the mixture in
cylinders. The obtained METAS-2017 primary calibration scales are made of 11
cylinders containing these five substances at near-ambient and slightly
varying molar fractions. Each prepared molar fraction is traceable to the
realisation of SI units (International System of Units) and is assigned
an uncertainty estimate following international guidelines (JCGM, 2008),
ranging from 0.6 % for SF6 to 1.3 % (k = 2) for all other
substances. The smallest uncertainty obtained for SF6 is mostly explained
by the high substance purity level in the permeator and the low SF6
contamination of the matrix gas. The measured internal consistency of the
suite ranges from 0.23 % for SF6 to 1.1 % for HFO-1234yf (k=1). The
expanded uncertainty after verification (i.e. measurement of the cylinders
vs.
each others) ranges from 1 to 2 % (k = 2). This work combines the advantages of SI-traceable reference gas mixture
preparation with a calibration scale system for its use as anchor by a
monitoring network. Such a combined system supports maximising compatibility
within the network while linking all reference values to the SI and assigning
carefully estimated uncertainties. For SF6, comparison of the METAS-2017 calibration scale with the scale
prepared by SIO (Scripps Institution of Oceanography, SIO-05) shows excellent
concordance, the ratio METAS-2017 / SIO-05 being 1.002. For HFC-125, the
METAS-2017 calibration scale is measured as 7 % lower than SIO-14; for
HFO-1234yf, it is 9 % lower than Empa-2013. No other scale for HCFC-132b was
available for comparison. Finally, for CFC-13 the METAS-2017 primary
calibration scale is 5 % higher than the interim calibration scale
(Interim-98) that was in use within the Advanced Global Atmospheric Gases
Experiment (AGAGE) network before adopting the scale established in the
present work.
The effect of intercontinental transport on measurements of nitrogen oxides (NOx), peroxyacetyl nitrate (PAN) and reactive nitrogen species (NOy) at the high altitude site Jungfraujoch (3580 m asl), ...Switzerland, was evaluated using a combination of backward trajectories and chemical filters (NOy to carbon monoxide (CO) ratio). Mixing ratios associated with air masses transported from the planetary boundary layers (PBL) of the three continental source regions Europe, North America, and Asia, and of free tropospheric origin were characterized. The analysis was applied to PAN, NOx and NOy measurements of the period 1997–1998, and to a period more than 10 years later covering several months in 2008 and 2009–2010. The results show that the mixing ratios of PAN, NOx and NOy are largest in air advected from the European PBL. In contrast to previous studies, our results indicate that the springtime maximum in PAN and NOy mixing ratios is largely attributable to air originating from the European PBL whereas air of free tropospheric origin and intercontinental transport contribute less significantly. PAN and NOy mixing ratios in air masses classified as free tropospheric are also highest in spring but substantially lower than those influenced by European PBL air. Air masses last influenced by the North American source region show considerably lower mixing ratios of nitrogen species than European air masses suggesting that a large fraction of NOy is removed during intercontinental transport probably due to washout of soluble species such as HNO3. The seasonal contributions from different source regions to PAN mixing ratios at Jungfraujoch were evaluated. The average European contribution is highest during the warm seasons with 47–57% in 1997–1998 and 61–69% in 2009–2010. The maximum contribution of North American air masses is also observed in the warm season and was about 5–7% in 1997–1998 and 6–10% in 2009–2010. Air from Asian source regions did not make a significant contribution due to the limited number of cases of direct transport from Asia, but when they occurred the air masses contained significant pollutant levels.
► We evaluated the effect of intercontinental vs. regional transport on PAN, NOx & NOy. ► Springtime maximum in PAN and NOy is attributable to European PBL than other sources. ► Spring maximum caused by strong photochemical activity with enhanced vertical transport. ► North American air masses had about a factor 2 lower mixing ratios than the European PBL.
PDF
